Project Summary. Colorectal cancer (CRC) is the 2nd leading cause of cancer death in the US, though CRC death can be reduced by screening. However, there is uncertainty as to which screening strategy is most clinically and cost-effective from a population perspective where the aim is to optimize completion of the entire screening process continuum. Modeling studies suggest benefits and harms of colonoscopy and stool blood test strategies are similar, but generally assume 100% participation and subsequent clinically appropriate follow up?something never achieved in clinical practice. Comparative effectiveness studies of testing strategies, including comparisons of specific tests and approaches to optimizing effective test use, are necessary. Safety-net health systems care for populations at increased risk for adverse CRC outcomes, such as the uninsured and minorities, and have more limited resources. Therefore, safety-nets must resolve the uncertainty regarding the most effective screening strategy. We will conduct a system-level, randomized comparative effectiveness trial of the benefits, harms, and costs of 3 screening strategies over 3 years, among 6000 patients age 50-64 years, who are not up-to-date with CRC screening, served by a large safety net health system. The three strategies studied will be: 1) Fecal immunochemical testing, with annual mailed invitation outreach (including a test kit), and a centralized process to promote participation and complete clinical follow up (FIT); 2) Colonoscopy, with annual mailed invitation outreach, and a centralized process to promote participation and complete clinical follow up (Colo); 3) Usual Care, with no mailed invitation outreach, and screening offered at primary care visits. The primary measure of benefit will be an outcome measure that summarizes patient-specific effective screening successes. The primary measure of harm will be screening non-participation. The primary measure of cost will be cost per-patient effectively screened. Our specific aims are to: 1) Compare benefits, harms, and costs of a FIT strategy versus a Colo strategy for CRC screening among patients not up-to-date with screening, and 2) Compare benefits, harms, and costs of a) the FIT strategy vs. Usual Care and b) the Colo strategy vs. Usual Care for CRC screening.